Certain agricultural products, such as potatoes, which grow under the ground, may need to be separated from clods and stones before being marketed. There is described in Applicant/Assignee's published German patent application Ser. No. P 33 06 769.4 apparatus for separation of a mixture of soil clods from potatoes by bouncing the mixture to be separated on a cylindrical drum. This apparatus operates on the basis of a difference of about 0.4 in the restitution coefficient of the potatoes and soil clods. The aforesaid apparatus has met with considerable commercial success.
The separation of potatoes from stones is not achieved by the apparatus of the aforesaid German Patent Application, since the restitution coefficients of potatoes and stones against a rigid surface are nearly the same, and the restitution coefficient of the stones normally may even exceed that of the potatoes.